Sensitive tube leakage circuit



Jan. 11, 1955 J. A. PERIALE SENSITIVE TUBE LEAKAGE CIRCUIT Filed Aug. 3, 1951 B-I- ZO INVENTOR.

JOHN A. PERIALE United States Patent SENSITIVE TUBE LEAKAGE CIRCUIT John A. Perlale, Belmar, N. J., assignor to the United States of America as represented by the Secretary of the Army Application August 3, 1951, Serial No. 240,261 6 Claims. (Cl. 324-24) (Granted under Title 35, U. S. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment of any royalty thereon.

il1is invention relates to test equipment for electron discharge devices and more particularly to apparatus for lndicatmg a current flow in the vacuous space between elements of an electron discharge device.

The object of this invention is to provide a simplified means for determining the existence of a current flow in the vacuous space between the elements of an electron discharge device.

Known circuits and test apparatus apply relatively high voltage to the elements of devices undergoing test, resulting in damage to said devices. It is a further object of this invention to avoid the possibility of such damage which is done by using a bias voltage as a testing voltage andapplying the amplified bias voltage to an indicating section by means of an amplifying stage, thus reducing the test voltage to a small fraction of the voltage presently applied by known test apparatus.

it is well known that in an electron discharge device with a heated cathode, there may be a minute current flow in the vacuous space between the cathode and the associated cold electrode despite the fact that the cold electrode is maintained at a negative potential relative to the cathode. This is due to the fact that a small percentage of electrons emitted from the cathode have a high initial velocity and will strike the cold electrodes. However, this current flow, in a properly constructed discharge device, will be extremely low, that is, in the order of a few microamperes, and will not etfect the normal operation of the device. However, if the electrodes, or the placement thereof, are off tolerance, the current flow will rise above an allowable value. Therefore, a further object of this invention is to provide a means for determining whether the current flow between the elements of an electron discharge device is above this allowable value.

Other objects of this invention will appear in the following description and appended claims, reference being had to the appended drawing consisting of one figure.

In the appended drawing, one embodiment of the invention, as it could be used with a pentode tube 30 as the electron discharge device undergoing test, is shown. Those skilled in the art will readily see that the invention will perform its function on electron discharge devices of any number of elements with minor circuit variations and without departing from the spirit of the invention.

The appended drawing shows an amplifying triode 10 connected to a positive plate voltage 20 and in series with a limiting resistor 11, and a neon glow tube 12. In parallel with the foregoing circuit is a biasing network consisting of a negative voltage supply 21 and resistors 13, 14 and 15 wherein resistor 15 is connected in parallel with glow tube 12 and resistor 11, resistor 14 is connected across grid 16 and cathode 17 of tube 10, and resistor 13 is connected in series with resistor 14 and a negative voltage source. Bias resistor 14 is connected in parallel with switching network 18. Switching network 18 consists of two selective switches 19 and 22 mechanically interlocked so that any switch set ting on one switch will have one and only one corresponding switch setting on the other switch. For simplicity, the switches are shown side by side and their mechanical interlock is indicated. Switch 19 consists of rotatable arm 23 permanently connected to one end 2,699,528 Patented Jan. 11, 1955 of bias resistor 14 and fixed plate 25 composed of some insulating material and having contact points 26 corresponding to and electrically connected with the elements of the electron discharge device undergoing test. Arm 23 selectively makes contact with points 20 when rotated. owitch 22 consists of rotatable plate 24 composed of some conducting material and lixed plate 27 composed of some insulating material in which are mounted contact points 28 corresponding to and electrically connected with the elements of the electron discharge device undergoing test. Rotatable plate 24 has notch 29 so that it normally makes contact with all but one element of the electron discharge device undergoing test and ties them all electrically to the opposite end or bias resistor 14 to which arm 23 of switch 19 is connected. "this is true for all positions of plate 24 except the one illustrated. in the illustrated position of plate 24, notch 29 serves to isolate the connection of heater 33 with point 32 while plate 24 ties the remaining elements of tube 30 to arm 23 and consequently to point 31. In thismanner, one element of the electron. discharge device undergoing test is always electrically connected to one end or resistor 14 while all other elements of said electron discharge device are connected to the opposite end of resistor 14. Switches 19 and 22 are operated in conjunction so that the one element that switch 19 connects to resistor 14 is the one element that switch 22 does not connect to the opposite end of resistor 14. Although many systems of mechanical interlock will suggest themselves to persons skilled in the art, one method of obtaining the desired conjunctive relationship is to mount, in fixed relation, rotatable arm 23 of switch 19 and rotatable plate 24 of switch 22 on the same shaft with switches 19 and 22 mounted along the axial length of said shaft.

To test an electron discharge device according to the invention, the device is placed into the described circuit in the same manner as pentode tube 30. Rotatable arm 23 and rotatable disk 24 of switches 19 and 22 respectively are conjunctively revolved so that the elements of said discharge device are successively and singly connected to one end of resistor 14. Each successive element is selectively connected to point 31 by arm 23, and all other elements of said discharge device are connected by rotatable disk 24 to point 32 at the other end of resistor 14 which puts any leakage path between elements of the electron discharge device in parallel with bias resistor'14. This is true for all positions of arm 23 and notch 29 except the one illustrated. In the illustrated position of arm 23 and notch 29, one element of the electron discharge device undergoing test is connected to point 32 while all other elements of said electron discharge device are interconnected by plate 24 to point 31 through wires 34 and 35 and arm 23. Thus as arm 23 and plate 24 are rotated through all positions, one element of the electron discharge device undergoing test is always electrically connected to one end of resistor 14 while all other elements of said electron discharge device are connected to the opposite end of resistor 14. Bias voltage is developed across resistor 14 through the circuit composed of negative potential 21, resistors 13, 14, 15 and ground. The bias voltage developed across resistor 14 normally holds amplifying tube 10 at cut-off but in the event that there is a current flow in the vacuous space between the elements of the electron discharge device undergoing test, the selective rotation of arm 23 and disk 24 places the current flow path in parallel with resistor 14 causing a. drop in the voltage developed in resistor 14 which in. turn causes the negative bias voltage on tube 10 to decrease and thus allows tube 10 to conduct. The conduction of tube 10 coupled with the increased current drawn by reslstor 15 because of the effective decrease in resistance of resistor 14 in the bias circuit due to the parallel leakage path with resistor 14 causes a greater voltage to appear across resistor 15 which in turn causes glow tube 12 to so that the cathode of tube 30 is heated to a point where it thermionically emits electrons.

'lhose skilled in the art will realize that various indicating means such as a meter in place of the glow tube shown or a voltmeter across tube may be used without departing from the spirit of this invention.

As many apparently widely difierent embodiments of the invention may be made without departing from the spirit and scope hereof, it is to be understood that the invention is not listed to its specific embodiments except as defined in the appended claims.

what is claimed is:

1. In an apparatus for indicating a current flow between elements of an electron discharge device, said device including a plurality of cold electrodes at least one of which is to be tested and a cathode heated to thermionically emit electrons: the combination comprising an amplifier tube having at least an anode, a cathode coupled to a point of rer'erence potential, and a control electrode; an anode-cathode circuit for said tube including a source of direct current voltage for maintaining the anode thereof at a positive potential relative to the cathode thereof and means for indicating an anodecathode current through said tube exceeding a given value; a biasing network connected between the control electrode and cathode of said tube providing a direct current negative bias voltage for rendering the control electrode at a negative potential relative to the cathode thereof sufiicient to maintain the quiescent magnitude of the anode-cathode current of said tube below said given value; and coupling means for connecting all of said electrodes except the electrode under test to tht cathode of said electron discharge device, and for con necting the cathode of said amplifier tube, and for further connecting the electrode under test to said control electrode of said amplifier, whereby a current flow between the electrode under test and the cathode of said device, in excess of a predetermined value, reduces the negative potential upon the control electrode of said tube, causing said anode-cathode current to rise above said given value and resulting in an indication on said indicating means.

2. In an apparatus as set forth in claim 1, wherein said electron discharge device further comprises a heater connected to a source of voltage for heating the cathode thereof; and wherein said coupling means comprises means for connecting said heater to the cathode of said tube, and switch means for selectively disconnecting the cathode of said electron discharge device from the cathode of said tube and connecting it to the control electrode of said tube.

3. In an apparatus as set forth in claim 1, wherein said indicating means comprises a glow tube and a first resistor connected in series between the cathode of said tube and said point of reference potential, and a second resistor connected in parallel with said glow tube and first resistor.

4. In an apparatus as set forth in claim 3, wherein said biasing network comprises a third resistor connected between the control electrode and cathode of said tube, and a relatively high impedance source of potential connected to said control electrode for maintaining said control electrode negative with respect to said cathode of said tube.

5. In an apparatus for indicating a current flow between elements of a multi-electrode discharge device including a plurality of cold electrodes, a heater and a cathode heated by said heater to thermionically emit electrons: the combination comprising an amplifier tube having at least an anode, a cathode, and a control electrode; an anode-cathode circuit for said tube including a source of direct-current voltage having positive and negative terminals for maintaining the anode thereof at a positive potential relative to the cathode thereof, an indicating means comprising a glow tube and a first resistor connected in series between the cathode of said tube and the negative terminal of said voltage source, and a second resistor shunting said glow tube and first resistor, said indicating means indicating leakage of said device in excess of a predetermined value in response to an anode-cathode current through said tube exceeding a given value; a biasing network comprising a third resistor, said third resistor being connected between the control electrode and cathode of said amplifier tube, and a high impedance source of direct current negative potential connected to the control electrode of said amplifying tube sutficient to maintain the quiescent magnitude of the anode-cathode current of said tube below said given value; means connecting the heater of said discharge device to the cathode of said amplifier tube; and a multi-position switch means which in one position thereof connects said plurality of cold electrodes and cathode of said tube to the control electrode of said amplifier tube, and in all other positions thereof selectively connects a cold electrode under test to the control electrode of said amplifier tube and the remaining cold electrodes and the cathode of said device to said heater.

6. In an apparatus for indicating a current flow between elements of an electron discharge device, said device including a plurality of electrodes under test, one of said electrodes being a cathode, and a heater for causing said cathode to emit electrons, the combination comprising: an amplifier tube having at least an anode, a cathode coupled to a point of reference potential, and a control electrode; an anode-cathode circuit for said amplifier including a source of direct current voltage for maintaining the anode thereof at a positive potential with respect to the cathode, and means for indicating an anode-cathode current through said tube exceeding a given value; a network for biassing said control electrode with a direct current negative potential sutficient to maintain the quiescent magnitude of the anodecathode current of said amplifier below said given value, and coupling means for connecting at least the one electrode under test in said device to the control electrode of said amplifier, and for connecting the heater of said device to the cathode of said amplifier, and for further connecting the remaining cold electrodes to the cathode of said electron discharge device.

References Cited in the file of this patent UNITED STATES PATENTS Ammeters, pages 480 and 481.

Reich, Theory and Applications of Electron Tubes, Second edition, McGraw-Hill Book Co. Inc., New York, 1944, 15-11 Vacuum-Tube Ammeters, pages 6l2-618. 

